FIG. 1 shows a typical arrangement where multiple gas turbine engines or skids, numbered 1-5, are operated at a single site. The operation of each engine is controlled by its electronic control unit 6, which in turn receives commands from a master controller 7. The master controller 7 governs the operation of the entire site and for example will control a compressor 8 which receives fuel from a tank 9 and flows the pressurized fuel to each of the engines 1-5. In response to a variety of inputs, the master controller starts and stops the five engines as needed.
Maintenance costs associated with gas turbine engines are a major concern of operators of such engines. Great efforts are taken to predict what the costs will be and to reduce these costs as much as possible by performing routine maintenance at periodic intervals. Where multiple engines are located at a single site, predictable maintenance is important for logistical reasons as well issues such as plant availability and spare parts availability. Generally, these engines will age together and reach predetermined maintenance intervals at the same time. As result, the operator may have to absorb large maintenance costs within a short period of time and could also lose plant availability if all the engines need service at the same time.
For example, assume the engines 1-5 have a recommended time between overhauls of 30,000 hours and the annual average load at the site is 25,000 hours per year, (5000 hours per engine per year). If the engines are started by the youngest age when load demand increases, then all engines will age at the same rate and reach the 30,000-hour limit within a few months of each other. In this scenario, the owner would have to pay for several overhauls in one year and possibly lose plant availability during the time all five engines are being overhauled.
Unless all five engines are needed all the time, the master controller can be programmed to select which engines to start as power demand increases, and which to stop when power demand decreases. Accordingly, there is a need for a method of selecting which engines to start and stop so that the engines reach their maintenance interval in a nonrandom manner thus making maintenance costs predictable and minimizing the downtime for the site.